Re: [seccomp] Request for a "enable on execve" mode for Seccomp filters

[Kees Cook]

On Wed, Oct 28, 2020 at 01:42:13PM +0100, Jann Horn wrote:
> +luto just in case he has opinions on this
> 
> On Wed, Oct 28, 2020 at 12:18 PM Camille Mougey <commial@xxxxxxxxx> wrote:
> > From my understanding, there is no way to delay the activation of
> > seccomp filters, for instance "until an _execve_ call".
> > [...]
> > It would also ensure there is only one thread running
> > at the filter enabling time.
> 
> You're alluding to cases where library constructor functions launch
> threads? Is that a thing anyone does? (And in case someone does it, we
> still have TSYNC, so I don't think this would be a real problem.)

Unfortunately, yes, it happens. TSYNC got designed specifically to
"recapture" these constructor-launched threads. :( It was a common enough
situation Chrome wanted to solve due to some weird GPU libraries that
did this during init before Chrome was running.

-- 
Kees Cook